1. Field
The present disclosure relates to an image forming apparatus such as a printer, multifunction machine, photocopier, facsimile apparatus, or the like including a resist part for curling and sending out paper.
2. Description of Related Art
An image forming apparatus has a paper feeding part (for example, a paper cassette) for accommodating a plurality of sheets of paper. The image forming apparatus conveys paper supplied from the paper feeding part, and forms an image on the paper. A roller or the like is provided in a conveyance path for conveying the paper. At this time, the risk of delays in paper feeding or paper conveying from roller slippage, reduced conveying capacity due to roller wear, or the like arises. Delays in feeding or conveying the paper reduce the productivity of the image forming apparatus. In regard whereto, there are known paper conveying apparatuses used to ensure productivity despite diminished roller conveying ability.
Specifically, there is known a paper conveying apparatus having a paper sensor for detecting whether paper is present in a paper conveying part, the apparatus configured so as to measure a time T from when a paper feeding start signal is given to when the paper sensor detects the leading end of the paper during paper feeding, compare the detected time T to a predetermined value T0 set in advance when two or more sheets of paper are continuously fed, and perform a control so that the timing at which paper feeding of the second and subsequent sheets of paper is begun is advanced by an amount of time equal to T-T0. Such a configuration advances the timing at which paper feeding begins by the amount of time equal to T-T0, thereby attempting to prevent increases in roller slippage over time and reductions in paper line speed.
An image forming apparatus may be provided with a resist part (resist roller pair) upstream of an image-forming part in the paper conveyance direction. The resist part sends out paper at a suitable timing The resist part is also used, for example, to correct improperly squared (skewed) paper. Specifically, the leading end of the paper strikes the stopped resist part. Curl is then generated by continuing paper conveyance on the following end side of the paper. The elasticity of the bent paper forces the leading end of the paper to line up with the nip formed by the resist part, correcting the skew of the paper.
Conventionally, the curl of the paper is generated by stopping the resist part and continuing to convey the leading end side of the paper using a paper feeding roller or a conveying roller (intermediate roller) located one position upstream of the resist part.
In the paper conveying apparatus described above, the timing at which paper feeding is begun is advanced only on the basis of the detected time T. However, the position of the paper within the paper feeding part may vary. For example, the next sheet of paper may be dragged along due to friction from the previous sheet of paper, so that the paper is fed with the position of its leading end shifted towards the downstream side of the paper conveyance direction. When the paper in the paper feeding part is fed with the position of its leading end shifted towards the downstream side of the paper conveyance direction, the paper feeding reaches the resist part prematurely. When this happens, any delay in paper conveyance is cancelled out by the feeding and conveyance of the paper having begun from a downstream-shifted position. As a result, no delay or advance in paper conveying may be determined to be present.
Correction of the paper feeding start timing according to the method of the paper conveying apparatus described above is greatly affected by variations in the position of the leading end of the paper in the paper feeding part, with no consideration whatsoever being given to the sheet interval of the conveyed paper. There is thus the problem that delays or advances in the timing at which the paper arrives at the resist part cannot be correctly determined. The correction performed by the paper conveying apparatus described above is also greatly affected by variations in the position of the leading end of the paper in the paper feeding part. There is the problem that such paper feeding start timing correction may create a sheet interval that is too small.